Hearing devices are portable hearing apparatuses which are used to provide hearing assistance to the hearing-impaired. In order to accommodate the multiplicity of individual requirements, different designs of hearing devices are provided, including behind-the-ear hearing devices (BTE), in-the-ear hearing devices (ITE) and concha hearing devices. The hearing devices cited by way of example are worn on the outer ear or in the auditory canal. In addition to these, however, bone conduction hearing aids as well as implantable or vibrotactile hearing aids are also available on the market. The damaged hearing is herewith stimulated either mechanically or electrically.
Essential components of the hearing devices include in principle an input transducer, an amplifier and an output transducer. The input transducer is typically a receiving transducer, e.g. a microphone and/or an electromagnetic receiver, e.g. an induction coil. The output transducer is mostly realized as an electroacoustic converter, e.g. a miniature loudspeaker, or as an electromechanical converter, e.g. a bone conduction receiver. The amplifier is usually integrated into a signal processing unit. This basic configuration is shown in FIG. 1 by way of the example of a behind-the-ear hearing device. One or more microphones 2 for recording the ambient sound are incorporated in a hearing device housing 1 that is designed to be worn behind the ear. A signal processing unit 3, which is likewise integrated into the hearing device housing 1, processes the microphone signals and amplifies them. The output signal of the signal processing unit 3 is transmitted to a loudspeaker and/or receiver 4, which outputs an acoustic signal. In certain cases the sound is transmitted to the ear drum of the hearing device wearer via a sound tube which is secured in the auditory canal by means of an otoplastic. The hearing device and in particular the signal processing unit 3 are supplied with power by means of a battery 5 which is likewise integrated into the hearing device housing 1.
Modulatable LC oscillator circuits are used for the energy-efficient realization of a wireless data transmission between hearing devices. The LC circuit can be used here both for receiving as well as for transmitting. The frequency-determining components of such circuits must nevertheless be precisely attuned to the desired values. Deviations from the desired value, which are caused by means of manufacturing tolerances, can be corrected by a one-off trimming of the resonance circuit during the manufacturing process. The influence of temperature effects and parameter drift as a result of ageing is however not covered thereby. Special modulation methods such as QPSK or BPSK for instance nevertheless require a high absolute precision of the frequency, which also requires a compensation of temperature effects and ageing.
With hearing devices, which are to be exclusively wirelessly programmable (without a conventional programming interface), it is also problematical that the wireless programming is only then possible when the LC circuit of the wireless hearing devices transmit/receive circuit has already been correctly trimmed. Controlling the trimming by means of an external programming device is in this way not possible.
With previous hearing devices, a modulation method is used for data transmission, the precision requirements of which can be fulfilled with a one-off trimming during the manufacturing process. The LC oscillator is started here and the current oscillator frequency is measured by a frequency counter integrated onto the hearing device chip. This measurement value can then be read out by way of the programming interface. The PC used for programming determines the capacity value required for compensation from the deviation from the desired value. A programmable capacity matrix which is likewise integrated onto the chips applies this capacity value, said capacity matrix now likewise being configured by the PC by way of the programming interface.
Tietze, U.; Schenk; Ch.: Halbleiter-Schaltungstechnik, [Semiconductor circuit technology], Edition 11, Berlin [inter alia]: Springer, 1999, pages 1284-1286, ISBN 3-540-64192-0 discloses a phase locked loop (PLL). Its aim consists of adjusting the frequency of an oscillator such that it corresponds to the frequency of a reference oscillator, and in fact so precisely that the phase shift does not run away. A phase locked loop can be realized for instance with the aid of a voltage-controlled oscillator.
The article Kral, A.; Behbahani, F.; Abidi, A. A.: RF-CMOS oscillators with switched tuning. In: Proceedings of the IEEE 1998, Custom Integrated Circuits Conference, 1998, pages 555-558 discloses an RF-CMOS oscillator, which can be tuned using a connectable capacitor.